Taipei – The organiser of a party which saw a fireball rip through a Taiwan waterpark leaving 15 dead was found guilty of negligence on Tuesday and jailed for almost five years, as the court paid tribute to the "excruciating pain and torment" of the bereaved.Lu Chung-chi, owner of Colour Play Asia, was behind the event at Formosa Fun Coast where coloured corn starch being sprayed on around 1 000 partygoers ignited under the heat of stage lights last June, sending them running for their lives and leaving hundreds injured.He was found guilty of negligence causing death at Taipei's Shihlin district court as relatives of the victims gathered outside waving banners calling for justice.Judge Kuo Hui-ling read the verdict with no further comment – Lu was not in court.A press statement from the court released after the verdict paid tribute to the young victims of the tragedy."Most of the victims were very young and their wonderful lives were about to start. They had beautiful dreams to be realised," it said."Because of the explosion, 15 of them lost their lives and most of the survivors suffer tremendous physical and emotional pain and torment."Relatives of the deceased suddenly lost their family members and suffered irreparable and excruciating pain and regret," it added."The explosion happened due to the negligence of the defendant," the statement said.The case has angered grieving relatives and the families of the injured as only Lu was indicted over the disaster. He was one of nine people investigated, including the chairperson and president of the water park.Calls for justiceCampaigners have urged prosecutors to open a new investigation into the accident, with a group of 50 rallying outside court on Tuesday, waving banners saying: "Return Justice and Fairness to Me."Some said they were pleased with the verdict, but that the sentence was not long enough. The charge of negligence leading to death carries a maximum sentence of five years."At least the charges were held up, but this is not enough for the relatives. Four years and 10 months is too little," said Julie Wang, spokesperson for a victims' association. Her 21-year-old son suffered 55% burns.The high prosecutors' office told AFP on Tuesday it had ordered a district court to reopen the investigation into the other eight originally investigated.Almost 500 partygoers were injured in the blast, more than 200 of them seriously. Horrific video footage showed revellers – most of them between 18 and 25-years-old – screaming as they tried to escape.Some were left with more than 90% burns in some cases leading to amputations, with many still enduring painful rehabilitation.Medics described it as an unprecedented disaster for Taiwan, given the scale and severity of the injuries.Specialists from Japan were flown in to advise on the treatment of the seriously injured and Taiwan undertook the grisly but necessary task of importing metres of skin for grafts.The only undamaged skin on some survivors' bodies were the parts covered by their swimsuits.An investigation showed the hottest parts of the stage lights hit temperatures of more than 1 000 degrees Celsius, while the powder's ignition point was just 500 degrees Celsius.One mother, Chen Lu-yu, whose student son died in the disaster, called for the "real perpetrators" to be brought to justice outside court on Tuesday.She said the family had donated her son's organs after his death in the hope that it would enable others to have a "happy and healthy" life."I see other families, other people holding grandchildren," she told AFP."My son will never have a chance again, he will never have a chance to live out his dreams."